Foams having urethane groups which are obtained by the reaction of polyisocyanates with polyether and/or polyester polyols are known and widely used. The possibilities of application, particularly of the polyether foams, are, however, severely restricted in certain fields since they are unsuitable for flame lamination and high frequency (HF) welding. Fields in which these properties are particularly desirable include, for example, the manufacture by flame laminating of composite systems having surface layers of foils and/or textiles. Such composite systems are, in many cases, subsequently contoured and/or shaped by high frequency welding.
It is known that foams which are intrinsically capable of being flame laminated and also to a certain extent high frequency welded can be obtained from polyisocyanates and polyester polyols with the addition of suitable auxiliary agents and additives. These foams can, however, only be produced on special machines and are inferior to polyether-polyurethanes in some of their properties such as the openness of their cells, their elasticity and their resistance to moisture and heat.
It is also known that polyurethane foams capable of being flame laminated and high frequency welded can be prepared from polyether polyols, polyisocyanates, water and/or blowing agents in the presence of emulsifiers, stabilizers, catalyst and other additives by the addition of special auxiliary agents.
U.S. Pat. No. 3,205,120 describes the preparation of flame laminating polyether-polyurethane foams by the addition of a minor quantity of a polyol having a molecular weight of from 200 to 1500. Polyols containing phosphorus such as tris-(dipropylene glycol)-phosphite are said to be particularly suitable. One disadvantage of this process is that processing becomes less reliable and there is a certain tendency for the core of the foam to discolor. Moreover, if conventional quantities are used, the flame laminating characteristics obtained are distinctly inferior to those of a polyester-polyurethane foam.
U.S. Pat. No. 4,060,439 discloses the inclusion in the foam formulations for flexible polyether foams of small quantities of alkylene glycols having from 2 to 8 carbon atoms or the inclusion of triols having from 3 to 10 carbon atoms, of dialkanolamines having from 2 to 10 carbon atoms, or of short chain glycol ethers and of polyvalent phenols. It has been found in practice, however, that the inclusion of such compounds in the foam formulations makes foaming more difficult and provides only a very narrow margin of operation between producing open pores and closed pores.
In view of the disadvantages described above of polyether-polyurethane foams (which explain why polyester-polyurethane foams are mostly used for flame laminating and high frequency welding), there is a great demand for a polyurethane foam which is reliable in production and capable of being flame laminated and high frequency welded.
It has now surprisingly been found that, in contrast to the compounds described in U.S. Pat. No. 4,060,439, hydroxy-pivalic acid neopentylglycol esters included in formulations for the production of flexible polyether-polyurethane foams do not result in closed cells nor in processing difficulties but, rather, give rise to an optimally open-celled elastic flexible foam which has excellent mechanical properties, is very suitable for flame laminating and can also be high frequency welded to a certain extent.